Azoethane photolysis

This might be the case since the full mercury arc was used in this series of experiments. Vibrationally nonequilibrated ethyl radicals were observed in azoethane photolysis at the shorter wavelength (5). It is expected that the rate constant for the reaction of a thermally equilibrated isobutyl radical with oxygen will be nearly equal to that for the ethyl radical. Certainly one should accept the present estimate of k7 + k as a lower limit of the value for thermally equilibrated isobutyl radicals. We plan to test the order of the reaction more extensively and redetermine k7 + kg using the flash photolysis technique employed in the methyl (21) and ethyl (5) radical studies with oxygen to shed further light on this problem. 

The photolysis of a mixture of oxygen-18, diethyl ketone, and azoethane under conditions in which only the azoethane absorbed did not result in the formation of diethyl ketone-18. In other words, ethyl radicals are not sufficient to lead to the formation of diethyl ketone-18. 

Bartlett and Engel investigated the liquid phase direct and sensitized photolysis of 2,2 -azoisobutane. They showed that direct photolysis and singlet photosensitization were efficient to induce decomposition of azoisobutane (at 20 °C) but triplet photosensitization was not. The measured values of quantum yields were surprisingly large, values obtained in the photolysis of azomethane, azoethane or azoisopropane under similar conditions. 

On the basis of these results combined with Worsham and Rice s suggestion that in the azoethane reaction the decomposition state cannot be the vibrationally excited ground state, Calvert et al. strongly argued in favor of an excited triplet decomposition state for the photolysis of azoalkanes, although the possibility of the involvement of more than one triplet was not considered. 

It is gratifying to find that the ratios (0 43 and 0-35, respectively) of the rate constants for disproportionation and coupling, equal to the ratio of the percentages of C2H4 and C4H10, are close to the ones reported for a range of ten solvents (acetic acid was not included, however). These values fall between ethyl radicals produced by photolysis of azoethane at 65 C (Stefani, 1968). 

Thus, it has been studied azoethane decomposition [21] stimulated by ruby laser (/.=694.3nm) with power density equal to 70+175 MW/cm2. It has been established that the N2 yield is proportional to the order 2.2 0.1 with respect to the light intensity. The authors of [22] suppose that after photon absorption the excited molecules from the first excited singlet state A are transfered to an other excited singlet state B from which fluorescence is forbidden. The both states are at close range. The excited molecules which are on B level may be decomposed with a rate which depends on the nature of radicals linked with azo group. The authors of [23] assume that both mechanisms (thermo-and photo) are identic, but only in the case of photolysis transfer to triplet (T) state is possible. 

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